Apparatus for preparation of metals and alloys of improved purity level



Sept. 8, 1964 w. J. PENNINGTON ETAL 3,148,237 APPARATUS FOR PREPARATION OF METALS AND ALLOYS OF IMPROVED PURITY LEVEL Filed Feb. 17, 1960 2 Sheets-Sheet 2 I INVENTORS m; L/AMJ. AFN/WWW W/44 444/ .1 Mail #M/V TH E I R 47'7'0MEY6 United States Patent 3,143,237 APPARATUS FOR PRERARATHGN 0F METALS AND ALLQYS 0F IMPRQVED PURITY LEVEL William James Pennington, Venetia, and William Joseph McElhaney, Imperial, Pa, assignors to Universal- Cyclops Steel Corporation, Bridgeville, Pa, 21 corporation of Pennsylvania Filed Feb. 17, 1960, Ser. No. 9,347 4 Claims. (Cl. 266-34) This invention relates to apparatus and a method for the preparation of metals and alloys that are characterized by improved purity level compared to that heretofore obtained.

Certain contaminants in a metal or alloy have heretofore been known to be detrimental to their properties. It has been recognized in the metal industry that the higher the level of harmful trace contaminants such as nitrogen, oxygen and the like, the more detrimental their influences on the properties of the metals or alloys and more especially on the properties of such metals and alloys when used at high temperatures. For this reason means for reducing the level of such harmful contaminants have been sought over many years.

Metal melting practices and equipment have been aimed at obtaining the maximum purity level in the resulting product. One of the earliest means of accomplishing this was merely to mix or rabble the metal by hand using rods or stirrers after which the undesirable gangue or scum formed on the top of the metal would be skimmed off. The simple hand mixing developed into mechanical devices for agitating the molten bath for the purpose of bringing about reactions which would tend to eliminate at least some small portion of the undesirable contaminants. Other methods aimed also at removing such undesirable contaminants were the use of lances through which inert gases were passed to bubble through the molten bath, thus agitating or exposing the molten metal so that reactions could take place to further purify the metal. Induction coils have also been used as a means of stirring or agitating the bath. Superheating the bath was also intended to bring about a reduction of harmful contaminants. Pouring of metal into large molds to allow the impurities to levitate during solidification was another method. More recently super-sonic equipment has been developed to act as a stirring or agitating means.

Experience has shown that these previously employed methods or apparatuses do not remove the harmful contaminants to a degree necessary for the purity level desired in the type of metals produced today. They allow a certain amount of the detrimental elements that form inclusions or otherwise adversely affect the product to remain in the metal. Also a percentage of atomically dispersed gases remain in the metal following these treatments. These entrapped gases and the other elements which form undesirable oxides or other compounds to a largetextent remain in the metal. Apparatuses or methods for reducing the undesirable contaminant content have continually been sought either through removing such materials during the melting process or by preventing entry into the molten metal. Reduction of the contaminant level would improve the workability, fatigue, high temperature, magnetic, as well as other characteristics of the metals or alloys.

It is, therefore, the primary object of this present invention to provide an apparatus and method for the preparation of metals and alloys whereby such metals and alloys can be produced to a higher degree of purity than heretofore possible.

A further objective is to accomplish the primary object by means less complicated than those presently being used.

A further object is to accomplish the necessary purity without increasing the cost of the metals or alloys.

These objects are obtained in accordance with our invention in which a metal, capable of reacting with the harmful contaminants that subsequently become trace contaminants, is maintained in close association with the surface of the molten metals or alloys during the melting period. Such a metal is referred to as a reaction means in this specification. In this general manner we have been able to prevent trace contaminants, in the raw materials and in the atmosphere surrounding the molten metals or alloys being produced, from entering the metal since they react first with the reaction means and thus a lesser quantity is available for reacting with the molten bath. Accordingly there results a product that is of higher purity level than has heretofore been obtained.

The invention will be described in detail in conjunction with the attached drawings in which:

FIG. 1 is a front view of melting apparatus, with part of the chamber side wall cut away, displaying a reaction means in accordance with this invention;

FIG. 2 is a side view of the melting apparatus of FIG. 1; and

FIG. 3 is a top view of the melting apparatus of FIG. 1.

Referring now to the drawings, the numeral 10 indicates a conventional vacuum chamber in which high temperature metals and alloys can be prepared. Within the chamber 10 is a melting crucible or furnace 12. While the type of melting furnace used is of no particular criticality with respect to the present invention, that shown is the ordinary induction heating type now in general use. Heat is supplied to the induction heating furnace 12 by means of power from a source (not shown) connected to the cables 14 and 16 leading to the side wall 15 of the furnace 12. While they cannot be seen, the cables 14 and 16 terminate in coils about the furnace whereby a current can be induced into the metal within furnace 12, thus providing the heat necessary to melt the metal being processed.

In normal vacuum operation, it is conventional to pour the melt into a mold within the vacuum chamber. For this purpose, the furnace 12 is suspended within the chamber by beams 18 and 19. A flange 20, attached to the back of furnace 12 and which extends over the side of the beams, supports the furnace in an upright position at its back. The furnace is suspended at its front from the beams by suitable pins 22 and 23 rigidly attached to the furnace and which mate with bearings 24 and 25 afiixed to the beams 18 and 19. The pins and bearings permit rotation or tilting of the furnace to a position such as is shown by the dotted lines 26 in FIG. 2 so that the melt can be poured.

Melt poured from the furnace 12 is guided by a spout 28 on the mouth 30 of the furnace. During the melting process the mouth may be substantially closed by a cover plate 32. The cover plate is used largely to prevent radiation of heat from the melt, rather than actually to close the mouth of the furnace; therefore, the plate 32 only loosely fits the furnace mouth and may, but need not be perforated. The cover plate 32 is provided with a lever arrangement, such as a rod 34 attached to the cover and extending through the wall of chamber 10 so that manipulation from outside the furnace is possible. Consequently, the cover plate 32 can be moved away from the furnace mouth at the time the melt is to be poured or the furnace is to be charged. The dotted lines 34a in FIG. 2 show one position for the plate when it is not on the furnace mouth. A mold 40 is provided to receive melt poured from the furnace.

Attached to the upper surface of the cover plate 32 is a coil 36 composed of a reactive metal such as, but not limited to, titanium or zirconium, since other materials could be used if desired. This coil is the reaction means previously mentioned. In operation, the metal coil may be resistance heated; for this reason cable leads 3'7 and 38 are provided so that a power source (not shown) can be attached to the coil. While a coil-shaped reaction means is illustrated, it should be appreciated that a ribbon, a flat band or other arrangement can be used as well.

In the present invention, the reaction means functions to immobilize impurities, such as nitrogen and oxygen. Immobilization occurs through the formation of substantially stable nitrides or oxides of the metal of the reaction means, or by an absorption or other combination of the impurities with that means. To achieve the greatest benefits, the reaction means is heated to a temperature that promotes maximum immobilization. The temperature used depends, of course, upon the particular impurity or impurities involved as well as the metal of which the reaction means is formed.

In a typical use of our invention, for example, in a vacuum induction melting process, a suitable furnace is charged and enclosed in a vacuum chamber, with a reaction means in place as above described. The chamber is pumped down to the operating pressure. The charge is then heated while power is supplied to the reaction means to heat it to the desired temperature at which it will scavenge the surrounding atmosphere of nitrogen, oxygen, and the like. Consequently, when the metal is fully melted and is held at temperature, a minimum of nitrogen and oxygen originating from either the atmosphere or the raw materials Will be available to combine with the melt for then it will have become bound in the reaction means and held there.

In testing the present invention, several nickel-base alloy heats were made having a composition, by weight, of 0.05 percent of carbon, 19.50 percent of chromium, 4.25 percent of molybdenum, 13.50 percent of cobalt, 3.00 percent of titanium, 1.30 percent of aluminum, 0.005 percent of boron, 0.06 percent of Zirconium and the remainder nickel. These heats were prepared according to usual vacuum induction melting procedures and poured into molds within the furnace.

In a first heat of this alloy, the reaction coil was not used. In other words, usual vacuum induction techniques were employed. In a second heat, the reaction coil, maintained within the temperature range of 1750 to 1800 F., was placed directly over the surface of the melt in the furnace and thereafter the melt was poured into a mold in the furnace. The third heat was prepared with the reaction coil, at 1700 to 2200 F., located behind and above the ingot mold during pouring. In the fourth heat the reaction coil, heated to the range of 2130 to 2240 F. and located on a furnace cover, as described above, was used. The resulting alloys were then examined for purity and rated with the Null; procedure described in Metals Progress, August 1958, pages 103 et seq. The purity ratings obtained are as follows:

Heat: Purity rating 1 -1.0 B 2 1-1.0 -C 3 11.0 F 4 l-1.0 B

From these purity data, it is evident that the reaction coil effectively improved the quality of the alloys as is attested by comparing the rating of heats 2, 3, or 4 with heat 1. Moreover, it is evident that this advantage is to be had in vacuum operations without regard to where the reaction means is located.

The coils used in the foregoing examples were composed of titanium. Actual analysis of the coil used for heat 4 before use in the system showed a nitrogen content of 0.009 weight percent. A cross-section sample of the coil was analyzed after use and found to have a nitrogen content of 0.013 weight percent. A residue i.- found on the surface of the coil after use contained 0.28 weight percent of nitrogen. Similarly actual analysis before use in the system showed an oxygen content of 0.24 weight percent. A cross-section sample of the coil was analyzed after use and found to have an oxygen content of 1.59 weight percent. A residue found on the surface of the coil after use contained 32.01% oxygen. These data are taken as proof that the reaction coil itself actually immobilizes the nitrogen and oxygen in the system.

Confirmation of the reproducibility was obtained by melting a series of ten heats of the composition previously given using the apparatus of this invention and evaluating their purity using the Nulk method. The ratings achieved are listed below:

Heat: Purity rating 5 30.0BC 6 20.0-D 7 1-1.0 -BC 8 5-2.0 -B 9 00.0A 10 2-1.0 -A 11 1-1.0 -A 12 2-1.0 -D 13 2-1.0 -C 14 4-1.2 D Average 2.2-0.82 BC A series of thirteen heats of the same composition melted without using the apparatus of this invention and evaluated by the same method as the above heats had the ratings listed below:

Heat: Purity rating 15 2l.2 CD 16 a- 31.2 -D 17 3-1 0 CD 18 31.3 -D 19 n- 2l.0 C 20 4-1.1 -C 21 3-1.0 CD 22 4l.3 CD 23 31.2 -D 24 10-2.5 CD 25 51.6 -D 26 7-1 7 CD 27 3l.2 -D Average 4.0-1.3 CD

The improvement obtained is quite obvious by a comparison of the above data.

In the foregoing description, the invention has been described With respect to its use in a vacuum system. However, it can be used as well where air melting is practiced. In air melting, the reaction means is used closely adjacent the melt surface rather than anywhere within the system as can be done in the vacuum practice.

According to the provisions of the patent statutes, We have explained the principle of our invention and have illustrated and described what we now consider to represent its best embodiment. However, we desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

We claim:

1. In a vacuum melting apparatus for preparing high temperature metals and alloys, including a vacuum chamber, a container in said chamber in which metal is melted, said container having a mouth for pouring molten metal, heating means for melting metal in said container, a cover movably mounted on the mouth of said container, and a mold for containing melt of said metal until it solidifies, the improvement of a non-consumable coil shaped reactive metal attached to said cover in the atmosphere therein which is in contact with said melt, and resistance heating means to heat said reactive metal to a temperature sufiicient to form a stable material with impurities within said chamber.

2. In an apparatus for preparing high temperature metals and metal alloys including a container in which said metal is melted, heating means for melting metal and producing a melt in said container and a mold for containing melt of said metal until it solidifies, the improvement of a non-consumable reactive metal shape movably mounted in said apparatus in the atmosphere therein which is in contact with said melt, said reactive metal shape comprising a metal selected from the group consisting of titanium and zirconium, said shape being mounted in close association with but not contacting said melt, and resistance heating means to heat said reactive metal shape to a temperature sufficient to form a stable material with impurities in the surrounding atmosphere that it is desired to keep from said melt.

3. In a vacuum melting apparatus for preparing high temperature metals and metal alloys, including a vacuum chamber, a container in which metal is melted, heating means for melting metal and producing a melt in said container, and a mold for containing melt of said metal until it solidifies, the improvement of a non-consumable reactive metal shape movably mounted in said chamber in the atmosphere therein which is in contact With said melt, said reactive metal shape comprising a metal selected from the group consisting of titanium and zirconium, said shape being mounted in close association with but not contacting said melt, and resistance heating means to heat said reactive metal shape to a temperature sufficient to form a stable material with impurities in the atmosphere within said chamber.

4. In a vacuum melting apparatus for preparing high temperature metals and metal alloys, including a vacuum chamber, a container in which metal is melted, heating means for melting metal and producing a melt in said container, and a mold for containing melt of said metal until it solidifies, the improvement comprising a cover that fits on the mouth of said container, said cover being movably mounted in said chamber in the atmosphere therein which is in contact with said melt, a non-consumable reactive metal shape attached to said cover, said shape and cover being mounted in close association with but not contacting said melt, and resistance heating means to heat said reactive metal shape to a temperature sufficient to form a stable material with impurities in the atmosphere Within said chamber.

References Cited in the file of this patent UNITED STATES PATENTS 2,205,854 Kroll June 25, 1940 2,427,339 Alexander Sept. 16, 1947 2,776,886 Kelly Jan. 8, 1957 3,026,195 Edstrom et al Mar. 20, 1962 

1. IN A VACUUM MELTING APPARATUS FOR PREPARING HIGH TEMPERATURE METALS AND ALLOYS, INCLUDING A VACUUM CHAMBER, A CONTAINER IN SAID CHAMBER IN WHICH METAL IS MELT/ ED, SAID CONTAINER HAVING A MOUTH FOR POURING MOLTEN METAL, HEATING MEANS FOR MELTING METAL IN SAID CONTAINER, A COVER MOVABLY MOUNTED ON THE MOUTH OF SAID CONTAINER, A COVER MOVABLY MOUNTED ON THE MOUTH OF SAID CONTAINER, AND A MOLD FOR CONTAINING MELT OF SAID METAL UNTIL IT SOLIDIFIES, THE IMPROVEMENT OF A NON-CONSUMABLE COIL SHAPED REACTIVE METAL ATTACHED TO SAID COVER IN THE ATMOSPHERE THEREIN WHICH IS IN CONTACT WITH SAID MELT, AND RESISTANCE HEATING MEANS TO HEAT SAID REACTIVE METAL TO A TEMPERATURE SUFFICIENT TO FORM A STABLE MATERIAL WITH IMPURITIES WITHIN SAID CHAMBER. 